Apparatus for reproducing images in natural color



May 20, 1958 J. l.. RENNICK A APPARATUS FOR REPRODUCING IMAGES IN NATURAL COLOR Filed May 14. 1951 2 Sheets-Sheet 1 2,835,727 APPARATUS FOR REPRODUCING IMAGES IN 'NATURAL COLOR Filed May 14, 1951 May 20, 1958 J. L. ENNICK 2 Sheets-Sheet 2 To Sync. Signal Cathode 56 Voltoge(Electrode 65 1o FIG. 6

INVENTORL" 'JoHN I .RENNIGK H l's AT United States Patent APPARATUS FR REPRODUCING lMiAGES IN NATURAL COLOR John L. Rennick, Elmwood Park, lll., assigner to Zenith Radio Corporation, a corporation of Illinois Application May 14, 1951, serial No. 226,125

3 Claims. (cl. 17a- 5.4)

This invention relates to television reception and more particularly to a novel method and apparatus for reproducing nuages in natural color. The invention is es pecially suited for utilizing information of the type produced and transmitted in the color television system disclosed in the copending application of lohn L. Renm'ck, Serial No. 215,761, led March 15, 1951, and assigned to the present assignee. For convenience, the invention will be described in that connection.

Picture information radiated by a transmitter such as the one disclosed in the aforementioned Rennick application defines a scanned subject in terms of two distinct characteristics, namely, brightness and color. The brightness information is derived by additively combining the output signals from three cameras, each adapted to produce a video signal representing one of the thre primary colors of the scanned subject. The resulting video signal is entirely free of color information and is generally similar to that of a conventional black-andwhite system.

The color content of the scanned subject is prescribed by a plurality of control signals, each representing the amplitude dierence between one of the three primary color signals and one-third the brightness video signal. These control signals are devoid of brightness informa tion and, because of the manner of their generation, they add to zero at every instant of time. Consequently, only two of the control signals need be utilized at the receiver in order completely to define hue and color saturation in the reproduced image. The afore-mentioned application describes in detail a receiver for reproducing color images by the use of three picture tubes and recognizes that one three-color tube may be utilized. Such a tube may include an electrode system for developing a single beam of electrons and a fluorescent screen having a plurality of triangularly shaped clusters of three luorescent elements, each emitting light of one of the primary colors in response to electron bombardment. The advantages of a system employing a single picture tube over those in which three picture tubes are required are self-evident.

It is an object of this invention to provide a novel method of and apparatus for reproducing television images in natural color in an improved system using a single picture tube.

In accordance with the invention, there is provided a television receiver for synthesizing an image in natural color in response to the arbre-described video and control signals. The receiver comprises an image-reproducing device including a single electrode system for developing a single beam of electrons and a liuorescent screen having a multiplicity of triangularly shaped clusters of three iluorescent elements. Each of these elements emits light of one of the three primary colors in response to electron bombardment. A deflection system is provided for controlling the position of the beam with respect to the target, and means-are included for applying sweep signals to the redaction system to effect scanning ICC of the target by the beam. beam as it scans the target, the system includes means for applying the brightness signal to the electrode system. The receiver further includes means for concurrently applying modified control signals havingrespective amplitudes inversely proportional to that of the bright-4 ness signal to the deflection system to effect angular and t radial displacement of the beam relative to a reference position in each of the clusters to determine the color contribution of each such cluster to an image in natural color. i

The features which are believed to be novel are set forth with particularity in the appended claims and the` invention, both as to its organization and manner of operation, together With further objects and advantages thereof may best be understoodl by reference to the following description taken in connection with the accom-l panying drawings in which:

Figure 1 is a block diagram, partly schematic, of a' complete television receiver for reproducing images in natural color according to the teachings of the present invention;

Figure 2 represents a segment of the target electrode of the arrangement of Figure l drawn to en enlarged A scale;

Figure 3 is a block diagram, partly schematic, of a modified arrangement of the receiver shown in Figure l; Figure 4 is a block diagram, partly schematic, of;

another modification of the receiver shown in Figure l;

Figure 5 is a graph useful in explaining the operation'v of a portion of the circuit of Figure 4; and,

Figure 6 is a block diagram, partly schematic, of still another modification of the receiver shown in Figure l. With reference now to Figure 1, the color'television electron-beam-forming electrode system 15 of an imagereproducing device 16 of the cathode-ray type which is. shown partially broken away to reveal deection ele-- Specifically, amplifier 14 isj coupled to the control electrode 17 and cathode 18 of electrode system 15 which additionally includes the usual focusing and accelerating electrodes` for directing a beam Y of electrons upon a fluorescent target screen 19 to be,

ments contained therein.

described more fully hereinafter.

Detector 13 is coupled to a synchronizing-signal separator 2li which separates the line and frame synchronizing signal components and supplies them to individualuoutput circuits coupled withk a scanning generator system l.

21. Generator 21 is of the type which produces the usual form of saw-tooth frame and line scanning signals in y each of two output circuits connected to frame dellection y plates 22 and line detiection plates 23 of tube'16.

The circuit as thus far described is generally similar -4 to a conventional superheterodyne type of television receiver and stages 11-14, 20 and 21 may be of any known construction. ln operation,` a radiated signal is intercepted by antenna 10 and applied to stage 11 where, after appropriate selection and amplification, it is converted to the intermediate frequency of the receiver; The intermediate-frequency signal is amplified in stage 12 and supplied to detector 13, wherein the video and synchronizing signal components are derived. The video-frequency components are amplified by amplifier 14 and-'appliedV to electrode system 15 of image tube 16 to control the intensity of the electron beam thereof. -Atthe Sametime, C

Patterned4 May 2o, 1915s In order to modulate the separator k2 0 separates the line and frame synchronizing signals of the received signal individually to synchronize the line and frame signal generating sections of stage 21. Thusfthe beam from electrode system `is deflected in synchronisrn with the synchronizing-signal components of the received signal to'trace a rectangular raster,.or a series of interlaced fields of spaced parallellines, upon screen 19-of image tube 16-as the beam intensity is varied in Vresponse vto the videoffrequency components thereby to--develop the light yanda shade values viewing screen.

Inorder to-,reproduce images in natural color, target 19 is comprisedv of a multiplicity of triangularly shaped clusters of three iluorescent disc-shaped elements. These elements individually emit' lightlof one of the primary colors in response-toelcctron bombardment. More specifically, the fluorescent .elements are `ot" likey area, substantiallyfilll the screen surface, and are arrayed so Athat thczelectrlon beam sees a succession of identically oriented clusters along each linetrace of ther scanning pattern. The several iluorescent elements are designated "R,.G, and B in lFigure 2l which representsl an enlarged sectionxof screen 19in the vicinity of the longi` tudinalgaxis 2 4 oftube 16 and which is illustrative offthe distribution of iluorescent elements over the entire screen. A Aplanar parallax member is Adisposed behind, or on the .electron gun sideot, screen 19 and is provided with a plurality of openings 26 shown in dash outline in Figure -2.. VVTThere is `one opening fork eachtriangular ycluster of screen 19 andeach of the. openings is centered with respect to theelectron beam path from gun 15 to the central portion of .itstassociated cluster.

several clusters.

The beam of electrons from electrode system v15, in oneoperating condition ofscanningpasses through successive'onesof theopenings 26 in approximatelyv perpendicular relation with Arespect to parallax member 25 to impinge vupon referencepositions centrally disposed relativelto each of the sevcraliluorescent clusters. Since Y leach-of the three fluorescent elements of every. cluster islequally excitedfin-this mode of operation,- the resulting light is of awhite quality.

In-order to alter thecolor-contributionof eachfluores-v f vcent element .to '.the Vlight produced by its cluster, it -is 'necessary to shift-the angle .of incidence of the Yelectron beam wtih respect tothe `=plane of Iparallax member 25. To that end, an auxiliary deflection system Aincluding `a plurality-of-deflection elements 30, 31k and' 32 is ydisposed Within the-neck-of tube 16 to provide, in the presence of l input signals,'adeflection ofthe beam of electrons from gun 15 transversely of axis 24-.vr Elements 30-32 are illustratcdfas pairsoffdeflecting plates, 'the axes of which are equi-angularly displaced about tubeaxisv24 so that the individuall deflecting-tield components of these plates- -i are 'displaced-'about thataxis. that although deflection `plates-have been shown, any

, equivalent arrangement may beemployed, for example, magnetiodeection coils. f

v Each ofthe plates -,32 maybe defined as a blue,

It is to beunderstood green-or red 'deflection element 'since theorientation of the-plates is'asuch tha'tlnpon the--applicationrof asignal to .anyone ofltheelenie'nts alone, -the beam of` electrons is deflectedY along a linelexten'din'g from the center-of one inimemb/er y25, Ha .convergence lcoil 33, coupled to a ksuitable .convergence signal source 34,is disposed Yabout Ythe of an imageV on the 2,835,727 e l J i The .openings have Y areas whichV correspond to that of the individual iluorescent elements and in Figure ,2 their outlines identify the neckrof tube lpbetween plates 30-,32 and plates 2K3 and 22.

It will be assumed that the receiver under consideration is to utilize the signal radiated by the transmitter of the ettore-mentioned copending application which contains, in addition to a 4 mcs. video band, color control control signals of lesser bandwidth, modulated upon different subcarriers interlaced in the video-frequency spectrum. That is to say, the color information is transmitted in interleaving relation with the brightness information so that the required bandwidth is but 4 mcs. This type of bandconserving method is generally well 'known and need not be described in detail.-

To derive these color control signals, detector 13 is coupled to three control signal channels 40, 41 and 42,V individually including a band pass filter in cascade with a detector and an amplifier. Each filter is arranged to pass, without attenuatiomthat portion of thel video spectrumwherein one color control signal is available so that each may be'said to be assigned to one ofthe blue, green and red color control signals and eachis coupledfutoan associated'one of pairs ofplates 30-32. The polarityY of signals applied tothe auxiliary defiectionplates 30- 4-,32 is such that for signals of 'like sense the deflection ofthe beam due to the field produced by each of the pairs is in the same direction with respect to the center of one of the clusters of fluorescent elements. In other words, a signal of positive polarity with respectto ground from any of the channels 40-42 produces a dellection ofthe beam in a direction from the center of one of the clusters toward the lluorescent'element of associated color. Thus channels 40-42 serve as the means for` concurrently api plying each of the color control signals V-to one ofthe deflection elements of the'aauxiliary deflection system 30-32 to eiiect angular :and radial displacementzof. the beam relative to a reference position centrally Yof Veach cluster to determine the color contribution cluster to an image in natural color. f

in operation, as the beam from electrode system 15 scans over the multiplicity of triangularly shapedfclusters of fluorescent elements it is modulated in intensity in accordance with the brightnesssignal as describedY hereinbefore. At the same timeVunder .the control of thesig-A nals from channels 40-42, .the beam is deflected angularly and radially relative toa central reference position in each cluster under the conjoint effect of the pluralityof control signals. Thus, the color contribution of yeach n cluster to an image in natural color is ldetermined. Specifically, the plates 30-32 serve to -establish a plurality of deflection fields in response toV the color :control signals and these individual deflection fields effectively combine to produce a resultant field which efects'the angular and Vradial displacement of the beam from the' center of a fluorescent cluster which is here referred to as a reference position.

It may be helpful in understanding the receiver to con` sider 'several specific examples of operation in connection withl a particular tluorescent cluster, namely,f'the` jone 'i aligned with opening 26 yof parallax member 25, as`v shown in Figure 2. By definition, each of the three color control signals is equal to the corresponding camera signal minus one-third the brightnesssignal. Hence, for v acolor condition in which .each of the three cameras contribute equally, that is to4 say, a black and white'picture is to be transmitted, the color control signals are zero in magnitude and the electron beam is not deflected w1th respect to the central reference' position in that cluster. Consequently, the beamy passes through opening 26 of parallax member 25 andrnpingesupon equal Since' the *three portions of each element of the cluster.l

primary colors are produced with equal relative interl- -sities, white light'is reproduced.

Let it be assumed now that at some operating interval the picture information being transmitted contains only *Y of veach such i a pure red color. -For that condition the ratios lof the red, blue and green camera signals are 1:0:0 and the brightness signal has a related magnitude of 1. Utilizing the relationship expressed earlier, it may be shown that the red color control signal has a magnitude of plus twothirds and the blue and green color control signals each have a magnitude of minus one-third. The resultant of the signals applied to the plates 30--32 and the tield of element 33 deilects the beam upwardly so that it impinges only upon the iluorescent element which emits red light. For the case of a diluted or less saturated red, under the control of plates 30-32, the electron beam impinges upon the clustenat some intermediate position between the red element and the central reference position. The same analysis is applicable for each of the other primary colors.

Let it now be assumed that a saturated purple color is required. For this operating condition, the green camera has zero output and the blue and red cameras have equal output signals with the result that red, blue and green control signals are in the relationship of Vs :Mu-17a. These color control signals cause the electron beam to strike the uorescent cluster so that the red and blue elements are equally excited, whereas the green element is inactive and the required purple color is reproduced. For a less saturated purple, a portion of the green element is excited corresponding to the degree of dilution.

There is thus available a gamut of colors, limited only by the purity of the red, green and blue primaries, and of which the dilution by white light may be controlled. Asr

the electron beam is scanned across the target and modulated in intensity to produce light and shade values, the color contribution of each cluster is varied in response to the color control signals as dictated by the color content of the image being scanned at the transmitter. Hence,

an image is synthesized in natural color on viewing screen 19.

As pointed out earlier, any two of the color control signals may be employed to define collectively hue and saturation of the reproduced image. The modified arrangement of Figure 3 is adapted to accomplish this. A picture tube 16 generally similar to the one employed in the circuit of Figure l is utilized, but in place of the rauxiliary deection system 30-32 two pairs of deecting plates 45 and l46 are associated with the tube. Pairs 45 and- 46 are disposed so that in the presence of signals thereon the electron beam is deflected along a line parallel to one of the sides of each triangular cluster. More specically, pair 45 is designated the .,green deection element and has an axis G and pair46 is designated the red deilection element and has an axis designated R. As illustrated in Figure 2, the projections along axis 24 of the axes G and R" intersect centrally of one of the uorescent clusters. The disposition of the axes of the plates is such that the bisector of the acute angle formed by their projections intercepts the blue fluorescent element of the cluster. Channel 40'is omitted and each of channels 41 (green) and 42'(red) is connected to the associated one of the pairs of plates 45 and 46. Signals from these channels are applied with such polarity that for signals of like sense the deection of the beam due to the eld produced by each of the pairs is in the same direction with respect to the center of one of the clusters.

The operation of the modied arrangement is generally similar to that described in connection with the circuit of Figure l. It may be shown that the color control signals from channels 41 and 42 completely define the position of the electron beam from electrode system with respect to a reference position in each of the clusters. For example, let it be assumed that the picture information being transmitted contains a pure red color. -As pointed out in connection with the discussion of this example for the circuit of Figure l, the resulting red color control signal has a magnitude of plus two-thirds and the green color control has a magnitude of minus one-third. The resultant of these two signals in connection with the field of convergence element 33 deects the beam upwardly so that it impinges only upon the uorescent element which emits red light; By a like analysis', it may be shown that an entire gamut of colors of required dilution may be produced. Consequently, the

two-color control system signal of Figure 3 may be eme ployed for the, synthesis of images in natural color.

The color control signals transmitted in accordance with the system of the aforementioned Rennick application may be defined as follows:

where Rc, Gc, and Bc are the respective color control signals; R0, G0 and B0 are thesignals developed by the red, green and blue cameras, respectively; and W is the brightness signal resulting from adding the three camera signals. These color control signals, when applied to a receiver constructed in accordance with the present invention, accurately determine color for brightness signals at maximum or near-maximum values whichthe system is designed to accommodate whereas reduced saturation accompanies brightness signals of substantially lesser values. This is understandablefrom an inspection of Equations a-c. It will be observed that the magnitude ot' each of the color control signals Re, Gc and Bc is related to the amplitude of the video signal W. As ai result, the amount of electron beam deection in a. direction from the central reference position of a fluorescent cluster varies directly with the magnitude of the` brightness signal. lesser in picture areas of lower intensity than in the brighter areas.

It has been demonstrated that insofar as color perception of the human eye is concerned, extreme accuracy of color reproduction is necessary only in the portion or portions of a viewed scene having maximum brightness. Consequently, the color-dilution which accompanics a reduction in brightness signal amplitude may' The circuit of Figure 4 represents a portion of the receiver shown in Figure l, anch identical elements are represented by the same reference numerals. A modulator 5@ is interposed between detector 13 and the blue, greeny and red channels 40-42 and comprises an electron tube 51 of the pentode type. A ground connection at terminal 52 and a lead extending between terminal 53,0f modulator 50 and detector 13 constitute a coupling circuit between these stages. connected to terminal 53 and the other end is grounded.

A control grid 55 of tube 51 is connected to the movable tap of potentiometer 54 and the cathode 56 of the tube Its anode 57 is connected through a load resistor 58 to the positive terminal of a B-supply sourceV 59, the negative terminal of which is grounded. The screen grid circuit of modulator `5t)includes a Ls creeri ,re-,V

is grounded.

Thus, for a given hue, color saturation isy One end of a. potentiometer 54 is nal Wi'llconta'in colorfcontrol components interleaved with video'V components Ainexcessfotone `megacycle in frequency. Thus, stage 67 is arranged to pass signal frequencies up to'. one megaoyclezso that only video componeuts are derived in its output circuit which is coupled to an input terminal 63y of stage 50 which, in turn, is

,grounded through a potentiometer 64, the movable tap of which is connected to th'esuppressor grid 65 of tube 51. 4The output signal of stage v5t)l is derived across load resistor 58 and'it appears `at-an, Voutput terminal 66 which is coupled to the input circuits of channels 40-42.

Thretcircuit parameters ,of stage 50 are arranged in knownfashion lto ,provide a control 'grid-to-plate transconductancethat 5 isginversely proportional to the modulating `potential .applied `between suppressor grid 65 and cathodey56. This type of characteristic is illustrated by the curve .of ,Figure 5 whichv is a =plot yof control Ygridplate .transconduotane .vs k Voltage; n .n

The operation... of a vcolor receiver incorporatingrthe modified `circuit of Figure 444m-'generally similar to that described in connection withV Figure l. Howeveninstead of signals being `.applied rdirectly from detector 13. to the blue, green yand red channels 40-42, the output signal of the detector is appliedvbctwcencontrol electrodeSS and cathode56 of-,electron `tube 51.4 At the same time, the lvideo-output .orbrightness signal from amplier 14 is inverted in phase and yfiltered to remove color information by unit 67. .'Ifhe'resulting signal is applied between suppressor grid 65 and cathode 56. .By .properly adjusting potentiometer controls 54 and 64, the outputy signal from stage 50 .contains modified color control signals individually equal tothe Yquotient of the received color l14 is'- suppressor grid-to-cathode control signalstaud one-.third thebrightness signal. In other words, the resulting vco'ntrolsignals derived from modulatorf and:designated Rm, .Gtm and Bmfmaybe defined as followsi mera-33K d @refiera (e).

Patina-3"; m

Accordingly, .color 'varia-tioris in lthe reproduced Aimage otherwise resultinglfromchanges `inl level `of vthe received brightness signal are -coinpensated and accurate color reproduction-iis achieved 4irrespective .of :the magnitude of the brightness. l

f As tan alternative-tothe the colorlcontrol signals .are.-modif'e`d simultaneously, it isV possible to modify ithese signals individually, after their separation fromone another.' Thisimay be ac- `complishedf-withnthe circuit arrangementofFigure 6 in conjunction witlrthe'receiverof'IFigure l. As in the embodiment yof :Figure il, three color channels :of essentially identical yconstruction.are-employed but, ffo'r convenience, only the blue channel 40 has been illustrated. It is coupled'to,anloutput-circuit ofdetector 13 and includes a baud` pass viilter andi-a detectorf connected in cascade with an amplifier-modulatorvStlf'which may be identical to stage 50 of -Figure"4.v Ajpha'se"inverter rand low-*pass ilter 67,` like Atheone of vFigure 4, is coupled between foregoing arrangement wherein' v invention.VV Y

the -video or brightnes'ssignal and-are finally presented as signals of the type dened by Equations ari-f. f

It `will"b 'e Aunderstoodl that the invention may be advantageously employed in. any color television system whereinbrightness information and color information are separately available at `the receiver'. i v

While particular embodiments of the present invention` have `been p-sh'ownand described, it will be obvious to those skilled inthe art that changes land modifications mayv be matierv without departing frorn-.-'thisinventionin its broader aspects, and, therefore, the aim in theap-y tions as `fall within il. A television yreceiver for `synthesizingLanimageliinf naturalcolor in response to a videosignal representing brightness information yderived by combining three priii` mary color signals and `in response to a'pluralitysof-fcon-j trol signals, collectively'dening hue and color saturaiv tionV and `individually representing the amplitudelfditfeience between one of said yprimary colorl signals and "ai portion of said video signal, said receiver Vcompri's'ingan.imageireproducing,device including a single electron gun for developing a single beam of electrons.andia-finosy rescent screen target having armultiplicitylof triangularly shaped clustersof three fluorescent elements individually emitting light of one .of the 4primary colors in response to. electron bombardment; .a deection systemfor controlling the position of said beam with respecbtosaid target; means for ,applying sweep signals to said deflection' system to effect scanning of said .target by saidlbearn; means for continuously applying said brightness signalk to said electron gunto modulate said beam asits'cans said'target; means Vfor imodifying the .amplitudelowsaidf control lsigna'lsrinversely'with respect to amplitude vari-A ations .fof 'said tvid'eo signal to deriveurnodiedcontrol; signals; andmeansffor concurrently applying said `rnodi. fied control signals to said deflection system `toleista'b# lish a resultant deiiectingf'eld for effecting angulara'ndf radial displacement of 4saidbeam relative to the centr l portion of eachlo'f said clusters to determine thelcolo'i'i contributioniofea'ch such cluster to -an image k.in natural4k color. l

. 2.v A :television receiver for vsynthesizing an image in natural color in response vto a video signal representing` brightness yinformation derived by combining Ithree pri i i mary color signalsl andin response kto a plurality yof con-'l trol signals, collectively defining hue and color saturation vand individually representing .the amplitude .difier-l ence between :one Vof said primary .color signalsandsa portion of-said video signal, said rcceivercomprising: :animage-reproducing device yincludinga single electrongun` forvdeveloping Va single beam lof electrons ,andaafluorescent screentarget` having a multiplicity .of triangularly.-

shaped clusters .off-three fluorescent elements kindividually f emitting 'light of one of the. primary colors in response Y` to electronbombardment;` a -deiectiony system lforgcon- -trolling theposition of -said beam with respect lto said" target; means for applying sweep signals to'said deflec-v tion-'systemic etfect scanning of said'target by said beam;` means *for continuously applying said brightnesspsigna'lg' to *said* electronvr gun `tol modulate said beam as `Tit scans;

said'targetg'a modulator for deriving the arithrnetical'lno]V p tient of the amplitude values of a pair of signals;`,x a1i' for applying said control signals andaty least a :portion of the'amplitude .of'said brightness signal to saidin' d'f. lator sirnultaneously,toy derive modified control havingrespective amplitudes inversely proportional to" that of said brightness signal; and means for concurrently applying said modilied control signals to said deflection system to establish a resultant deecting field for effecting angular and radial displacement of said beam relative to the central portion of each of said vclusters to determine the color contribution of each such cluster to an image in natural color.

3. A television receiver for synthesizing an image in natural color in response to a video signal representing brightness information derived by combining three primary color signals and in response to a plurality of color signals, collectively dening hue and color saturation and individually representing the amplitude diiierence between one of said primary color signals and a portion of said video signal, said receiver comprising: an image-reproducing device including a single electron gun for developing a single beam of electrons and a liuorescent screen target having a multiplicity of triangularly shaped clusters of three fluorescent elements individually emitting light of one of the primary colors in response to electron bombardment; a deilection system for controlling the position of said beam with respect to said target; means for applying sweep signals to said deflection system to etlect scanning of said target by said beam; means for continuously applying said brightness signal to said electrode gun to modulate said beam as it scans said target; a plurality of modulators for individually deriving the arithmetical quotient of the amplitude values of a pair of applied signals; means for applying said control signals to 10 respective ones of said modulators and for concurrently applying at least a portion of the amplitude of said brightness signal to said modulators to derive modified control signals having respective amplitudes inversely proportional to that of said brightness signal; and means for concurrently applying said modified control signals to said deflection system to establish a resultant defiecting iield for effecting angular and radial displacement of said beam relative to the central portion of each of said clusters to determine the color contribution of each such cluster to an image in natural color.

References Cited in the file of this patent UNTTED STATES PATENTS OTHER REFERENCES Television, volume Vl, T ri-Color Kinescope Receivers, pages 338442, published by RCA Review. 

